1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a manufacturing method of a color filter substrate for an LCD device.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are being developed as the next generation of display devices because they have advantageous characteristics such as light weight, thin profile, and low power consumption.
Active matrix liquid crystal display (AMLCD) devices include thin film transistors as switching devices for a plurality of pixels that independently control the pixels. Active matrix liquid crystal display devices have been widely adopted because of their high resolution and ability to display fast moving images.
In general, an LCD device is completed by manufacturing an array substrate and a color filter substrate and then interposing liquid crystal between the array substrate and the color filter substrate.
FIG. 1 is a perspective view illustrating a related art LCD device. In FIG. 1, the related art LCD device includes transparent lower and upper substrates 12 and 22 spaced apart from and facing each other. The LCD device further includes a liquid crystal layer 30 interposed therebetween.
Gate and data lines 14 and 16 are formed on an inner surface of the lower substrate 12 and cross each other to define pixel regions P. A thin film transistor T is formed at each crossing point of the gate and data lines 14 and 16. The thin film transistor T is connected to a pixel electrode 18 at each pixel region P.
A black matrix 25 is formed on an inner surface of the upper substrate 22 that faces the lower substrate. The black matrix 25 covers a non-display region, such as the gate lines 14, the data lines 16, and the thin film transistors T and has a lattice shape surrounding the pixel regions P. A color filter layer 26 is formed in each opening of the lattice of the black matrix 25. The color filter layer 26 includes red, green and blue color filter patterns 26a, 26b and 26c corresponding to the pixel regions P and sequentially and repeatedly arranged. A transparent common electrode 28 is formed on the black matrix 25 and the color filter layer 26.
The lower substrate 12 including the gate and data lines 14 and 16, the thin film transistors T and the pixel electrodes 18 may be referred to as an array substrate. The upper substrate 22 including the black matrix 25, the color filter layer 26 and the common electrode 28 may be referred to as a color filter substrate.
Although not shown in the figure, the array substrate and the color filter substrate are sealed by a sealant that is formed along peripheries of the two substrates to prevent the liquid crystal layer 30 from leaking. Lower and upper alignment layers are formed between the array substrate and the liquid crystal layer 30 and between the color filter substrate and the liquid crystal layer 30, respectively, and the lower and upper alignment layers determine an initial orientation of liquid crystal molecules. In addition, a polarizer is disposed on an outer surface of at least one of the substrates. Further, a backlight is disposed over the outer surface of the array substrate to provide light.
ON/OFF signals are sequentially applied to the gate lines 14, and an image signal is applied to the pixel electrode 18 in the selected pixel region P through the data line 16. An electric field perpendicular to the substrates is induced, and thus the liquid crystal molecules are driven by the electric field to thereby control light transmittance. Various images may be displayed by the varying light transmittance.
To improve viewing angles, an in-plane switching (IPS) LCD device has been proposed, in which the common electrode and the pixel electrode are formed on the same substrate. In the IPS LCD device, because the color filter substrate does not include the common electrode, the color filter substrate includes a black matrix, a color filter layer, and an overcoat layer. Moreover, to increase the brightness of the device and to more clearly produce the colors of the image, a four-sub pixel structure has been developed, wherein one pixel includes red, green, blue and white sub pixels.
FIG. 2 is a cross-sectional view of a color filter substrate for a related art LCD device having a four-sub pixel structure.
In FIG. 2, the color filter substrate further includes a white sub pixel. That is, red, green, blue and white color filter patterns 48a, 48b, 48c and 48d are formed on a substrate 41. The white color filter pattern 48d may be formed of a colorless transparent material. An overcoat layer 50 is formed on the red, green, blue and white color filter patterns 48a, 48b, 48c and 48d. The overcoat layer 50 has a flat surface. Patterned spacers 53 are formed on the overcoat layer 50 to keep the thickness of a liquid crystal layer (not shown) uniform.
FIGS. 3A to 3F are views illustrating a manufacturing method of a color filter substrate for an LCD device according to the related art.
In FIG. 3A, a black matrix 44 is formed on a transparent substrate 41 by applying or depositing a light-blocking material and patterning it by a mask process. The black matrix 44 includes first, second, third and fourth openings 46a, 46b, 46c and 46d and has a lattice shape.
In FIG. 3B, a red color filter layer (not shown) is formed on the black matrix 44 by applying photoresist including red pigments to substantially the entire surface of the substrate 41 and then by patterning the red color filter layer with a mask process to thereby form a red color filter pattern 48a in the first opening 46a. The red color filter pattern 48a partially overlaps the black matrix 44.
In FIG. 3C, a green color filter pattern 48b is formed in the second opening 46b by applying photoresist including green pigments to substantially the entire surface of the substrate 41 and then pattering it by a mask process. The green color filter pattern 48b partially overlaps the black matrix 44.
In FIG. 3D, a blue color filter pattern 48c is formed in the third opening 46c by the same process as the red and green color filter patterns 48a and 48b. 
In FIG. 3E, a white color filter pattern 48d is formed in the fourth opening 46d by applying colorless transparent photoresist to substantially the entire surface of the substrate 41 and patterning it by a mask process. The red, green, blue and white color filter patterns 48a, 48b, 48c and 48d constitute a color filter layer.
In FIG. 3F, an overcoat layer 50 is formed on the red, green, blue and white color filter patterns 48a, 48b, 48c and 48d by applying a colorless transparent organic material. The overcoat layer 50 protects the red, green, blue and white color filter patterns 48a, 48b, 48c and 48d and flattens the steps of the red, green, blue and white color filter patterns 48a, 48b, 48c and 48d. 
Next, patterned spacers 53 with column shapes are formed on the overcoat layer 50 by depositing a transparent organic material and patterning it with a mask process. The pattern spacers 53 have a thickness corresponding to a thickness of a liquid crystal layer (not shown), that is, a cell gap of an LCD device. The patterned spacers 53 are disposed over the black matrix 44 and spaced apart from each other.
In this manner, the related art color filter substrate having the four-sub pixel structure may be manufactured.
In order to manufacture the related art color filter substrate having the four-sub pixel structure, six mask processes are needed for patterning the black matrix 44, the red, green, blue and white color filter patterns 48a, 48b, 48c and 48d, and the patterned spacers 53. The mask process includes steps of light-exposing, developing, cleaning, etc. Therefore, the manufacturing processes and costs are increased, and the productivity is lowered as compared with a color filter substrate having only a three-sub pixel structure.